1. Field of the Invention
This invention relates generally to the field of microphones, and particularly to a method and apparatus for sensing audio signals that are sensitive to the audio signal but are insensitive to background noise.
2. Background Art
Prior art microphones generally operate under the principle of transducer action. Acoustic waves generated by one's vocal chords impinge on a transducer element, such as a diaphragm, piezo-electric crystal, or capacitor plate. The displacement of the transducer element caused by the acoustic waves is transformed into a corresponding electrical signal which is amplified for presentation or recording. For example, piezo-electrical crystal micrphones, variable-resistor class microphones, dynamic microphones, and condenser (also known as capacitor or electret) microphones all operate under the transducer theory that relies on pressure waves in the air or contact vibration sensing to convert speech into electrical signals.
One major drawback of prior art microphones is that they are sensitive to background noise. Accordingly, these prior art microphones are often less sensitive to the intended audio source. Furthermore, these prior art microphones are not easily adapted for use in many different situations because of their fixed placement. For example, many prior art microphones are mechanically mounted in a fixed location so they will not be able to receive the acoustic waves from a moving audio source in a consistent manner. As a further example, other prior art microphones are portable in that they may be worn by the talker, but these microphones suffer from the inconveniences associated with entangled and cluttered wires. Further, wireless microphones are subject to RF interference.
These prior art microphones typically exhibit tolerable performance in high signal and low noise environments. However, when the noise in an environment increases, the performance of these microphones degrades appreciably. In fact, in high noise environments, the signal to be recorded is often muffled or imperceptible because of the surrounding background noise. The signal to noise ratio (S/N) can degrade to a point that no meaningful audio information is recovered after demodulation.
Furthermore, as one increases the sensitivity of these prior art microphones to improve signal quality, these microphones also become more sensitive to the background noise. In other words, prior art microphones do not have the ability to differentiate between the audio signal and background noise.
Accordingly, there remains a need for a method and apparatus for sensing an audio signal that is sensitive to the audio signal but insensitive to background noise, and which provides improved signal quality.